As Lo-X said you'll have to update the size of the
sf::View or your
sf::RenderWindow.
That's what I've implemented in my code:
sf::Vector2f size = static_cast<sf::Vector2f>(mWindow.getSize());
// Minimum size
if(size.x < 800)
size.x = 800;
if(size.y < 600)
size.y = 600;
mWindow.setSize(static_cast<sf::Vector2u>(size));
mWindow.setView(sf::View(sf::FloatRect(0.f, 0.f, size.x, size.y)));
It gets called whenever the resize event (
event.type == sf::Event::Resized) is fired.
But keep in mind, if you want to change to fullscreen mode, you'll have to 'create a new videomode' with
window.create(...)